explaingit

hapijs/joi

★ 21,197JavaScriptAudience · developerComplexity · 2/5ActiveLicenseSetup · easy

TLDR

A JavaScript library for defining schemas and validating data against them. Validate objects, strings, numbers, and more with structured rules.

Mindmap

mindmap
  root((joi))
    What it does
      Define schemas
      Validate data
      Check objects
      Verify strings
    Use cases
      API input validation
      Form data checking
      Config file validation
      Type safety
    Tech stack
      JavaScript
      Node.js
      npm
    Audience
      Backend developers
      Full-stack engineers
      API builders

Things people build with this

USE CASE 1

Validate incoming API request data before processing it in your server.

USE CASE 2

Check form submissions match expected structure before saving to a database.

USE CASE 3

Ensure configuration files have required fields with correct types.

USE CASE 4

Verify user input meets constraints like email format or password strength.

Tech stack

JavaScriptNode.jsnpm

Getting it running

Difficulty · easy Time to first run · 5min
Use freely for any purpose, including commercial use, as long as you keep the copyright notice.

In plain English

joi is a data validation library for JavaScript. It lets you define schemas, structured descriptions of what your data should look like, and then validate objects, strings, numbers, and other values against those schemas. Based on the description and topics, it is designed to be the most powerful schema description and data validation tool in the JavaScript ecosystem, and is associated with the hapi web framework ecosystem. It is installed via npm and full documentation is available at joi.dev. The README does not provide further detail beyond pointing to the documentation portal.

Copy-paste prompts

Prompt 1
Show me how to create a joi schema that validates a user object with email, password, and age fields.
Prompt 2
How do I use joi to validate an API request body and return custom error messages if validation fails?
Prompt 3
Create a joi schema for a product object with required name, price, and optional description fields.
Prompt 4
How can I validate that a string is a valid email address using joi?
Prompt 5
Show me how to chain joi validators to check that a number is between 1 and 100.
Open on GitHub → Explain another repo

Generated 2026-05-18 · Model: sonnet-4-6 · Verify against the repo before relying on details.